1. Field of the Invention
Embodiments of the present invention relate to the field of audio signal encoding/decoding, and more particularly, to an apparatus, medium, and method for losslessly encoding/decoding an audio signal while adjusting a bit rate.
2. Description of the Related Art
Lossless audio encoding may be classified into Meridian Lossless Audio Compression (MLP: Meridian Lossless Packing), Monkey's Audio, and Free Lossless Audio Coding (FLAC). In particular, the MLP (Meridian Lossless Packing) can be applied to Digital Versatile Disc-Audio (DVD-A). Recent increases in Internet network bandwidth have made it possible to provide large amounts of differing multimedia content. When providing audio services, lossless audio encoding is required. The European Union (EU) has already initiated digital audio broadcasting through a Digital Audio Broadcasting (DAB) system, and broadcasting stations or content providers have adopted lossless audio encoding for digital audio broadcasting. In this connection, the ISO/IEC 14496-3:2001/AMD 5, Audio Scalable to Lossless Coding (SLS) standard is being developed as a standard for lossless audio encoding by the Motion Picture Experts Group (MPEG). This standard also supports Fine Grain Scalability (FGS) and enables lossless audio compression.
The compression rate, which is the most important factor in a lossless audio compression technique, can be improved by removing redundant information from data. The redundant information may be estimated and removed from adjacent data, or removed using the context of the adjacent data.
It is assumed that integer Modified Discrete Cosine Transform (MDCT) coefficients show a Laplacian distribution. In this case, Golomb coding leads to the optimum result of coding and bit plane coding is further required to provide FGS. A combination of Golomb coding and bit plane coding is referred to as Bit Plane Golomb Coding (BPGC), which allows audio data to be compressed at an optimum rate and provide FGS. However, there is a case where the above assumption cannot be applied. Since BPGC is an algorithm based on the above assumption, it is impossible to achieve the optimum compression rate when the integer MDCT coefficients do not show the Laplacian distribution. Accordingly, there is a growing need for development of lossless audio encoding/decoding that can guarantee optimum compression rates regardless of whether the integer MDCT coefficients show the Laplacian distribution.